The present invention relates to a stake usable more especially, but not exclusively, for measuring the electric resistances of ground connections, of the type comprising a smooth cylindrical metal rod, which has a point at its lower end and to which is welded a helical screw thread.
Numerous stakes made from metal or another material are already known (see for example French Pat. Nos. 815 246 and 1 218 876, Canadian Pat. No. 919 378, Swiss Pat. No. 390 509, English Pat. No. 299,516 and German Pat. No. 2 105 388).
For measuring the electric resistances of ground connections, it is necessary to provide temporarily two auxiliairy ground connections, one serving for injecting the measuring current and the other for taking the reference potential. These ground connections are generally provided in the form of stakes which, in order to present an acceptable electric resistance, must be driven into the ground to a depth of the order of 40 to 50 cm. To carry out this operation in the different kinds of soils likely to be encountered, two types of stakes are at present used. The stakes of the first type are formed by a rod having a head at one end, the other end being pointed so as to facilitate penetration thereof into the ground. The stakes of this type have the disadvantage of requiring a hammer to drive them into the ground and it is difficult to remove them subsequently from the ground.
The stakes of the second type are in the form of an auger having at its upper end a transverse handle. They may be driven manually into the ground by associating, by means of said transverse handle, a rotational movement with the vertical driving pressure properly speaking. The stakes of this second type allow the prescribed driving depth to be attained in a great variety of soils, without the need for a hammer and, moreover, they may be easily removed subsequently. However, the stakes of this second type are generally formed by a forging, founding or welding operation which, on the one hand, is relatively expensive and, on the other hand, does not readily provide the optimum shape desirable. In particular, when a helical sheet-metal flange is welded to the rod, it must be welded over the whole of its length.